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            <h2 class="toc-title">目录</h2>
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        </div><article class="page single"><h1 class="single-title animated flipInX">@Async注解的方法所在bean不能注入到自身属性中</h1><div class="post-meta">
            <div class="post-meta-line"><span class="post-author"><a href="https://wlizhi.cc" title="Author" target="_blank" rel="noopener noreffer author" class="author"><i class="fas fa-user-circle fa-fw"></i>Wlizhi</a></span>&nbsp;<span class="post-category">收录于 <a href="/categories/spring/"><i class="far fa-folder fa-fw"></i>spring</a></span></div>
            <div class="post-meta-line"><i class="far fa-calendar-alt fa-fw"></i>&nbsp;<time datetime="2022-01-17">2022-01-17</time>&nbsp;<i class="fas fa-pencil-alt fa-fw"></i>&nbsp;约 1009 字&nbsp;
                <i class="far fa-clock fa-fw"></i>&nbsp;预计阅读 3 分钟&nbsp;<span id="/posts/spring/async-cannot-circular-dependency/" class="leancloud_visitors" data-flag-title="@Async注解的方法所在bean不能注入到自身属性中">
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  <ul>
    <li>
      <ul>
        <li><a href="#使用及问题">使用及问题</a></li>
        <li><a href="#原因">原因</a></li>
      </ul>
    </li>
  </ul>
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            </div><div class="content" id="content"><p>@Async注解的方法所属的spring bean，不能注入到自身的属性中。</p>
<h3 id="使用及问题">使用及问题</h3>
<p>使用<code>@Async</code>注解需要在配置类中声明<code>@EnableAsync</code>，以启动此注解的支持。</p>
<p>当我们开启了<code>@Async</code>，并循环依赖当前<code>bean</code>时，启动会报错<code>BeanCurrentlyInCreationException</code>。</p>
<p>解决方法，将这段异步逻辑单独抽取到另一个<code>bean</code>中。</p>
<p>案例代码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="nd">@Slf4j</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Service</span>
</span></span><span class="line"><span class="cl"><span class="c1">// TODO 即使加了懒加载，启动时不报错，但只要调用getBean()时，还是会报错。
</span></span></span><span class="line"><span class="cl"><span class="c1">//@Lazy
</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="kd">public</span> <span class="kd">class</span> <span class="nc">AsyncServiceImpl</span> <span class="kd">implements</span> <span class="n">AsyncService</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="nd">@Resource</span>
</span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="n">AsyncService</span> <span class="n">asyncService</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="nd">@Async</span>
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">asyncExecute</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="n">asyncService</span><span class="o">.</span><span class="na">execute</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">execute</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="n">log</span><span class="o">.</span><span class="na">info</span><span class="o">(</span><span class="s">&#34;异步执行业务代码...&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h3 id="原因">原因</h3>
<ol>
<li>看注解<code>@EnableAsync</code>的声明</li>
</ol>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">TYPE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Documented</span>
</span></span><span class="line"><span class="cl"><span class="c1">// TODO 这里导入了一个ImportSelector
</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="nd">@Import</span><span class="o">(</span><span class="n">AsyncConfigurationSelector</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="nd">@interface</span> <span class="n">EnableAsync</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="n">Class</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">&gt;</span> <span class="nf">annotation</span><span class="o">()</span> <span class="k">default</span> <span class="n">Annotation</span><span class="o">.</span><span class="na">class</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kt">boolean</span> <span class="nf">proxyTargetClass</span><span class="o">()</span> <span class="k">default</span> <span class="kc">false</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="n">AdviceMode</span> <span class="nf">mode</span><span class="o">()</span> <span class="k">default</span> <span class="n">AdviceMode</span><span class="o">.</span><span class="na">PROXY</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kt">int</span> <span class="nf">order</span><span class="o">()</span> <span class="k">default</span> <span class="n">Ordered</span><span class="o">.</span><span class="na">LOWEST_PRECEDENCE</span><span class="o">;</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><ol start="2">
<li><code>@Import(AsyncConfigurationSelector.class)</code>中，导入了一个<code>ImportSelector</code>。</li>
</ol>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">AsyncConfigurationSelector</span> <span class="kd">extends</span> <span class="n">AdviceModeImportSelector</span><span class="o">&lt;</span><span class="n">EnableAsync</span><span class="o">&gt;</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME</span> <span class="o">=</span>
</span></span><span class="line"><span class="cl">			<span class="s">&#34;org.springframework.scheduling.aspectj.AspectJAsyncConfiguration&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">String</span><span class="o">[]</span> <span class="nf">selectImports</span><span class="o">(</span><span class="n">AdviceMode</span> <span class="n">adviceMode</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">switch</span> <span class="o">(</span><span class="n">adviceMode</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">case</span> <span class="n">PROXY</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">			    <span class="c1">// TODO spring启动时，会加载这个类。这是一个 @Configuration 注解的类。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">return</span> <span class="k">new</span> <span class="n">String</span><span class="o">[]</span> <span class="o">{</span><span class="n">ProxyAsyncConfiguration</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getName</span><span class="o">()};</span>
</span></span><span class="line"><span class="cl">			<span class="k">case</span> <span class="n">ASPECTJ</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="k">new</span> <span class="n">String</span><span class="o">[]</span> <span class="o">{</span><span class="n">ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME</span><span class="o">};</span>
</span></span><span class="line"><span class="cl">			<span class="k">default</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><ol start="3">
<li>看配置类中加载了什么</li>
</ol>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="nd">@Configuration</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Role</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ProxyAsyncConfiguration</span> <span class="kd">extends</span> <span class="n">AbstractAsyncConfiguration</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Bean</span><span class="o">(</span><span class="n">name</span> <span class="o">=</span> <span class="n">TaskManagementConfigUtils</span><span class="o">.</span><span class="na">ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Role</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">AsyncAnnotationBeanPostProcessor</span> <span class="nf">asyncAdvisor</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">Assert</span><span class="o">.</span><span class="na">notNull</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">enableAsync</span><span class="o">,</span> <span class="s">&#34;@EnableAsync annotation metadata was not injected&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// TODO 异步注解bean处理器。所有@Async注解的方法，对应bean都会被它处理。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">AsyncAnnotationBeanPostProcessor</span> <span class="n">bpp</span> <span class="o">=</span> <span class="k">new</span> <span class="n">AsyncAnnotationBeanPostProcessor</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">bpp</span><span class="o">.</span><span class="na">configure</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">executor</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">exceptionHandler</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">Class</span><span class="o">&lt;?</span> <span class="kd">extends</span> <span class="n">Annotation</span><span class="o">&gt;</span> <span class="n">customAsyncAnnotation</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">enableAsync</span><span class="o">.</span><span class="na">getClass</span><span class="o">(</span><span class="s">&#34;annotation&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">customAsyncAnnotation</span> <span class="o">!=</span> <span class="n">AnnotationUtils</span><span class="o">.</span><span class="na">getDefaultValue</span><span class="o">(</span><span class="n">EnableAsync</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="s">&#34;annotation&#34;</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">bpp</span><span class="o">.</span><span class="na">setAsyncAnnotationType</span><span class="o">(</span><span class="n">customAsyncAnnotation</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="n">bpp</span><span class="o">.</span><span class="na">setProxyTargetClass</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">enableAsync</span><span class="o">.</span><span class="na">getBoolean</span><span class="o">(</span><span class="s">&#34;proxyTargetClass&#34;</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="n">bpp</span><span class="o">.</span><span class="na">setOrder</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">enableAsync</span><span class="o">.&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="n">getNumber</span><span class="o">(</span><span class="s">&#34;order&#34;</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">bpp</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><ol start="4">
<li>继承关系如下</li>
</ol>
<p><code>AsyncAnnotationBeanPostProcessor</code> extends <code>AbstractBeanFactoryAwareAdvisingPostProcessor</code> extends <code>AbstractAdvisingBeanPostProcessor</code> implements <code>BeanPostProcessor</code></p>
<p>查看源码，异步代理对象是在bean初始化之后生成的。</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AbstractAdvisingBeanPostProcessor</span> <span class="kd">extends</span> <span class="n">ProxyProcessorSupport</span> <span class="kd">implements</span> <span class="n">BeanPostProcessor</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">    <span class="cm">/**
</span></span></span><span class="line"><span class="cl"><span class="cm">     * TODO 此方法是bean实例创建、依赖注入、初始化方法执行后，才执行的。
</span></span></span><span class="line"><span class="cl"><span class="cm">     */</span>
</span></span><span class="line"><span class="cl">    <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">Object</span> <span class="nf">postProcessAfterInitialization</span><span class="o">(</span><span class="n">Object</span> <span class="n">bean</span><span class="o">,</span> <span class="n">String</span> <span class="n">beanName</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">advisor</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">||</span> <span class="n">bean</span> <span class="k">instanceof</span> <span class="n">AopInfrastructureBean</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="c1">// Ignore AOP infrastructure such as scoped proxies.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>            <span class="k">return</span> <span class="n">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">bean</span> <span class="k">instanceof</span> <span class="n">Advised</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">Advised</span> <span class="n">advised</span> <span class="o">=</span> <span class="o">(</span><span class="n">Advised</span><span class="o">)</span> <span class="n">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">            <span class="k">if</span> <span class="o">(!</span><span class="n">advised</span><span class="o">.</span><span class="na">isFrozen</span><span class="o">()</span> <span class="o">&amp;&amp;</span> <span class="n">isEligible</span><span class="o">(</span><span class="n">AopUtils</span><span class="o">.</span><span class="na">getTargetClass</span><span class="o">(</span><span class="n">bean</span><span class="o">)))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="c1">// Add our local Advisor to the existing proxy&#39;s Advisor chain...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>                <span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">beforeExistingAdvisors</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                    <span class="n">advised</span><span class="o">.</span><span class="na">addAdvisor</span><span class="o">(</span><span class="n">0</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">advisor</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                <span class="o">}</span> <span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                    <span class="n">advised</span><span class="o">.</span><span class="na">addAdvisor</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">advisor</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                <span class="o">}</span>
</span></span><span class="line"><span class="cl">                <span class="k">return</span> <span class="n">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="k">if</span> <span class="o">(</span><span class="n">isEligible</span><span class="o">(</span><span class="n">bean</span><span class="o">,</span> <span class="n">beanName</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">            <span class="n">ProxyFactory</span> <span class="n">proxyFactory</span> <span class="o">=</span> <span class="n">prepareProxyFactory</span><span class="o">(</span><span class="n">bean</span><span class="o">,</span> <span class="n">beanName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="k">if</span> <span class="o">(!</span><span class="n">proxyFactory</span><span class="o">.</span><span class="na">isProxyTargetClass</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">                <span class="n">evaluateProxyInterfaces</span><span class="o">(</span><span class="n">bean</span><span class="o">.</span><span class="na">getClass</span><span class="o">(),</span> <span class="n">proxyFactory</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="o">}</span>
</span></span><span class="line"><span class="cl">            <span class="n">proxyFactory</span><span class="o">.</span><span class="na">addAdvisor</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">advisor</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="n">customizeProxyFactory</span><span class="o">(</span><span class="n">proxyFactory</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="k">return</span> <span class="n">proxyFactory</span><span class="o">.</span><span class="na">getProxy</span><span class="o">(</span><span class="n">getProxyClassLoader</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">        <span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">        <span class="c1">// No proxy needed.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>        <span class="k">return</span> <span class="n">bean</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">    <span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>spring中bean实例创建后会提前暴露引用，所以在依赖注入之前可以获取到bean实例。也是基于此实现了循环依赖注入。</p>
<p>而<code>@Async</code>注解，是在依赖注入之后，才生成的代理对象，这是自相矛盾的。所以在使用<code>@Async</code>注解的方法所在类的<code>bean</code>不允许循环依赖注入。</p></div>

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